LAUSR

The orange-yellow and colorless essential oils with respective yields of 1.54% and 3.59% were extracted from the dry leaves of Cymbopogoncitratus (DC.) Stapf and Eucalyptus citriodora Hook. collected south of Brazzaville. Analysis by gas chromatography (GC) and by gas chromatography coupled with mass spectrometry (GC/MS) allowed the identification of fifteen (15) and eight (8) constituents representing (96.25%) and (98.46%) of total essential oils respectively. Cymbopogoncitratus oil consists mainly of geranial (51.99%) and neral (32.94%), two geometric isomers constituting citral which occupies a rate of 84.93%. While citronellal with a high level of (80.72%) and citronellol (10.48%) are the major compounds of the essential oil of Eucalyptus citriodora. Geranial (citral a) and citronellal 2,4-dinitrophenylhydrazones were hemi-synthesized by a simple, easy method, respectively from essential oils of Cymbopogoncitratus and Eucalyptus citriodora with respective conversion rate (yields) of 20%. and 37%, in a short time (three to five minutes). Analysis of geranial and citronellal 2,4-dinitrophenylhydrazones by UV-visible spectrophotometry showed maximum absorption wavelengths of 390 nm and 370 nm respectively. The UV-visible spectrophotometric method employed for the determination of these hydrazones is convenient, fast and simple. The hemi-synthesized hydrazones could be useful in the pharmaceutical industry, in perfumery, cosmetic and in biomedicine.